The construction of factory-made flexible HVAC ducts is well known in the industry. These types of ducts usually comprise a helical-supported duct liner (sometimes referred to as the core or inner core) covered by a layer of fiberglass insulation, which is, in turn, covered by a scrim-reinforced vapor barrier. Scrim is a woven material that adds strength to a laminate construction when made a part thereof. U.S. Pat. Nos. 6,158,477 and 5,785,091 show typical constructions of factory made ducts. U.S. Pat. No. 5,785,091 teaches that the duct liner and vapor barrier can be manufactured from polymer tapes, particularly polyester. U.S. Pat. No. 5,526,849 discloses a plastic helix in combination with a metal helix and U.S. Pat. No. 4,990,143 discloses a polyester helix. United States Patent Publication No. 2007/0131299 discloses a polyester scrim used in a vapor barrier.
In the prior art, factory-made flexible HVAC ducts are typically constructed of three main components; a duct liner for conveying air, a layer of insulation for preventing energy loss through the duct wall, and a vapor barrier for holding the fiberglass around the liner while protecting the fiberglass from moisture. The duct liner is commonly constructed of a steel wire sandwiched between layers of polyester (PET) film. Other plastics and coated fabrics are also used to construct the wall of the duct liner.
In the prior art, a plastic helix is sometimes used in conjunction with a steel helix to support the duct liner. In some cases, a narrow metal strip is crimped around the material forming the wall of the duct liner. The strip holds the material together and provides support.
Flexible tubing constructed of homogeneous materials is also common. These types of tubing have a similar support structure to that of a flexible duct liner with a spiral helix connected to a tube wall. These products are not known to be used as HVAC duct liners.
Flexible HVAC duct liners are composed of a mixture of materials, typically metals, plastics and/or fiberglass. The insulation is typically a batt of low-density fiberglass wrapped around the inner core. In some cases, other various textile scrap fiber is used to make the insulation batts. The insulation is held around the duct liner by the vapor barrier.
The vapor barrier is commonly constructed of either a tubular extruded polyethylene film or a fiberglass rip-stop, usually scrim, sandwiched between layers of polyester film. In the case of polyester films, the outer layer of film is typically a metallic-coated polyester film while the inner film is clear uncoated polyester film. In the prior art, a polyester scrim may be substituted for fiberglass scrim.
FIG. 1 shows an example of a prior art HVAC duct 10 that includes a duct liner 1, insulation layer 3, and vapor barrier 5. The duct liner comprises a polymer layer 7 surrounded by a metal helix 9. Although not shown, the vapor barrier is made up an inner clear polyester layer, a fiberglass scrim, and an outer metallized polyester layer.
Factory-made flexible HVAC ducts are aggregates of a number of materials. Ducts that contain a particular material or set of materials in the duct liner have different materials or sets of materials in the vapor barrier. This is a result of material selection based on cost and performance of the materials in meeting the test criteria of safety agencies (such as UL, ETL, etc.).
Mixed materials used in the duct liner and the vapor barrier of factory-made flexible HVAC ducts prohibit the recycling of any of the otherwise recyclable materials without separating the materials first. In cases where the duct liner or the vapor barrier were of a homogeneous material, they would not be compatible with the materials used in the other components and could not be recycled together in a common recycling stream. For example, extruded polyethylene vapor barrier is homogeneous, but it is not recyclable with materials used in the duct liner of factory-made flexible HVAC ducts. Factory-made flexible air ducts with polyester film vapor barrier are all fiberglass-scrim reinforced. The fiberglass scrim is not compatible for recycling with the polyester. The metallic-coated film used in most vapor barrier is not compatible for recycling with either the polyester film or the fiberglass scrim.
Another difficulty in this area is that factory-made flexible HVAC ducts are required to meet certain safety/performance criteria as defined by safety agencies and code bodies with jurisdiction where the products are being used. These criteria make the use of certain materials (especially plastics) extremely difficult for structural elements of the ducts. Manufacturing process and product design changes are necessary to overcome issues that otherwise prohibit conformance with safety/performance criteria.
The vapor barrier, insulation, and duct liner of a factory-made flexible HVAC duct can be easily separated from each other. The fiberglass insulation is recyclable once removed. However, it is not economically feasible to separate the components comprising the vapor barrier or the duct liner. It is cheaper to pay for landfill disposal than to separate the materials of these duct components. Therefore, it is normal industry practice to landfill all used or damaged HVAC ducts or sections of duct without recycling them. The environmental impact is substantial. It is estimate that approximately 140 million feet of insulated flexible HVAC duct is replaced (through demolition and/or renovation) each year in North America alone. The scrap duct also causes problems at landfills as the steel wire helices become entangled in equipment and often cause damage to the equipment.
Another environmental problem with these prior art ducts relates to the use of metal helices in the duct liner. The steel wire is the heaviest material in the duct and makes up more than half the weight of the duct. This requires more fuel for distribution than a lighter weight material would require. Also, the steel helices are often permanently deformed during the packaging of the ducts. This prohibits smaller packages from being used, which would also reduce the energy required for distribution. Once deformed, the steel helices can restrict airflow within the duct once it is installed, leading to further energy loss in the HVAC system.
When factory-made flexible HVAC ducts are cut either during manufacture or during installation, the cut ends of the steel helices have sharp ends responsible for puncture wounds and cuts to those manufacturing, installing and removing flexible ducts. The steel helices are cold-worked during the manufacturing process causing the material to “spring back” (recover) when the helices are cut during manufacturing, installation and removal. This effect often leads to a wound as the sharp points of the steel helices are propelled towards the hands or arms that are holding or supporting the ducts.
In the prior art, there are no flexible duct helices that are capable of recovering from deformation that would allow for potentially smaller packages and better airflow in HVAC systems.
In light of the problems with state of the art HVAC ducts, a need exists to provide improved duct designs in order to make the ducts more amenable to recycling rather than disposal in a landfill or the like. However, no factory-made flexible HVAC duct is offered with a duct liner of homogeneous material. In addition, no factory-made flexible HVAC duct with a duct liner and vapor barrier comprised of recyclable materials that would prevent the widespread landfill dumping of flexible duct scrap by allowing two or three separate compatible recycle streams is known in the prior art. Further, no factory-made flexible HVAC duct with a duct liner, vapor barrier, and insulation comprised of recyclable materials that would prevent the widespread landfill dumping of flexible duct scrap by allowing one compatible recycle stream is known in the prior art
In response to this need, the present invention provides an HVAC duct that overcome the problems in recycling and injury associated with the prior art duct liners. The HVAC duct of the invention has at least its duct liner and vapor barrier construction made from polymer materials that enable these two components to be recycled, thus avoiding the landfill and disposal problems of prior art duct liner. In a further embodiment, the invention provides for a flexible HVAC duct liner that is entirely recyclable. The duct liner also employs a polymer support structure that does not pose the problems associated with the metal helices of prior art ducts.